Move unused forked code to external directory (#1192)

* Move unused forked code to external directory

* Fix SLN build errors

* Add back resource provider core since it's referenced by main resource provider project

* Update PackageProjects step of pipeline

external/Microsoft.SqlTools.Hosting.UnitTests/TaskExtensions.cs

@@ -0,0 +1,26 @@
+
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System;
+using System.Threading.Tasks;
+
+namespace Microsoft.SqlTools.ServiceLayer.Test.Common
+{
+    public static class TaskExtensions 
+    {
+        public static async Task<Task> WithTimeout(this Task task, TimeSpan timeout)
+        {
+            Task delayTask = Task.Delay(timeout);
+            Task firstCompleted = await Task.WhenAny(task, delayTask);
+            if (firstCompleted == delayTask)
+            {
+                throw new Exception("Task timed out");
+            }
+
+            return task;
+        }
+    } 
+}